This invention relates to an improved method and apparatus for the recovery of hydrocarbon from oil shale, tar sands and heavy oil containing diatomaceous earth.
The term "oil shale" refers to sedimentary deposits containing organic materials which can be converted to shale oil. Oil shale can be found in various places throughout the world, especially in the United States in Colorado, Utah, and Wyoming. Some especially important deposits can be found in the Green River formation in the Piceance Basin, Garfield and Rio Blanco counties, in Northwestern Colorado.
Oil shale contains organic material called kerogen which is a solid carbonaceous material from which shale oil can be produced. Commonly oil shale deposits have variable richness of kerogen content, the oil shale generally being stratified in horizontal layers. Upon heating oil shale to a sufficient temperature, kerogen is decomposed and liquids and gases are formed. These fluids contain heating values and comprise shale oil, carbon monoxide, carbon dioxide, hydrogen, light hydrocarbon gases, water, hydrogen sulfide, and others.
Bitumens are hydrocarbon materials of natural or pyrogenous origin frequently found in liquid, semisolid or solid form. Tar sands containing various types of bitumen hydrocarbons exist in various areas of the world as, for example, the heavy deposits of Athabasca tar sands existing in Canada. These sands contain large reserves of bitumen type hydrocarbon constituents. For example, the bitumens or oil in the sands may vary from about 5 to 21% weight percent and generally occur in an amount of about 12% weight percent. The gravity of this bitumen or oil ranges from about 6.degree. to 10.degree. API with an average value generally of about 8.degree. API. These sands exist as beds ranging from about 100 to 400 feet thick below at least about 200 feet of overburden. A typical oil recovered from tar sands has an initial boiling point of about 300.degree. F. and about 50 weight percent of the oil boils above about 950.degree. F.
The term "tar sand" refers to a consolidated mixture. The sand in tar sand is mostly alpha quartz as determined from X-ray diffraction patterns. The bitumen or tar of the tar sands consists of a mixture of a variety of hydrocarbons and, if properly separated from the sand component, may be used as feedstock for the production of synthetic fuels and/or petrochemicals.
Tar sand deposits occur throughout the world, often in the same geographical areas as petroleum deposits. Significantly large tar sand deposits have been identified and mapped in Canada, Venezuela, and the United States. The Canadian tar sand deposits are known as the Athabasca tar sands and are located in the province of Alberta, Canada. The estimated reserves for the bitumen content in the Athabasca tar sands has been estimated to be approximately 900 billion barrels and, to date, is the only tar sand deposit in the world currently being mined and processed for the recovery of the bitumen content.
Analysis of the Athabasca tar sands indicates an average bitumen content of approximately 12-13% by weight. Importantly, the Athabasca tar sands also have a relatively high moisture content of approximately 3-5%, by weight, connate water. It has, therefore, been postulated by certain investigators that the equilibrium structure of the Athabasca tar sands consists of a sand mixed with but separated from the bitumen matrix by a film of connate water, the connate water surrounding each grain of sand. Accordingly, it is further postulated that the bitumen in the Athabasca tar sands has already been displaced from the sand grains by the connate water. Under these conditions, bitumen separation involves a relatively simple phase disengagement process whereby the bitumen phase is readily disengaged from the sand phase by the conventional hot water separation techniques.
A more comprehensive discussion of the Athabasca tar sands may be found in the literature including, for example, (1) E. D. Innes and J. V. D. Tear, "Canada's First Commercial Tar Sand Development," Proceedings of the Seventh World Petroleum Congress, Elsevier Publishing Co., 3, p. 633, (1967); (2) F. W. Camp, The Tar Sands of Alberta Canada, Second Edition, Cameron Engineering, Inc., Denver, Colo. (1974); and (3) J. Leja and C. W. Bowman, "Application of Thermodynamics to the Athabasca Tar Sands," Canadian Journal of Chemical Engineering, 46, p. 479, (1968).
Additionally, the following U.S. patents are a few of the patents which have been granted for apparatus for processes directed toward obtaining bitumen from tar sands: U.S. Pat. Nos. 1,497,607; 1,514,113; 2,871,180; 2,927,007; 2,965,557; 3,161,581; 3,392,105; 3,553,099; 3,560,371; 3,556,980; 3,605,975; 3,784,464; 3,847,789; 3,875,046; and 3,893,907.
According to a report by the Utah Geological and Mineral Survey, the State of Utah contains at least 25 billion barrels of bitumen in the form of Utah tar sands. This represents approximately 95% of the total mapped tar sand reserves in the United States. Although the Utah tar sand reserves appear small in comparison with the enormous potential of the Athabasca tar sands, the Utah tar sand reserves represent a significant energy resource when compared to the United States crude oil proven reserves (approximately 31.3 billion barrels) and the United States crude oil production of almost 3.0 billion barrels during 1976. Utah tar sands occur in six major deposits along the eastern edge of the state and bitumen content varies from deposit to deposit as well as within a given deposit. However, the current information available indicates that the Utah tar sand deposits average generally less than 10% bitumen by weight but have been found with a bitumen saturation of up to 17 percent by weight.
Importantly, unlike the Athabasca tar sands, Utah tar sands have been found to be so dry that no moisture content can be detected by standard analytical techniques. Accordingly, it is obvious that in the absence of connate water, the bitumen is directly in contact with and bonded to, the surface of the sand grains. In addition, tests have also determined that bitumen obtained from Utah tar sands is two orders of magnitude or about 100 times more viscous than bitumen obtained from Athabasca tar sands. Hence, processing of Utah tar sands must involve both bitumen displacement of the bonded bitumen from the sand grains and subsequent phase disengagement of the more viscous bitumen from the sand phase.
Another type of hydrocarbon bearing material similar to tar sands is heavy oil containing diatomaceous earth. Diatomaceous earth contains siliceous remains of marine life and has been found in association with crude oil, such as that found in California's McKittrick field, and reported in The Oil and Gas Journal, Dec. 18, 1978.
Oil can be recovered from these hydrocarbon bearing materials, oil shale, tar sands and oil containing diatomaceous earth, by thermal processes. Heating these materials to suitable temperature can result in oil being formed or released.
For example, oil shale can be retorted to form a hydrocarbon liquid either by in situ or surface retorting. In surface retorting, oil shale is mined from the ground, brought to the surface, crushed, and placed in vessels where it is contacted with hot heat transfer medium, such as hot shale or gases, or mixtures thereof, for heat transfer. The resulting high temperatures cause shale oil to be freed from the oil shale forming a partially spent oil shale comprising inorganic material and carbonaceous material commonly referred to as coke. The coke may be deposited on the surface of the shale particles and also within the shale particles. In addition to the coke, partially retorted kerogen, commonly referred to as bitumen, may be present. The carbonaceous material can be burned by contact with oxygen at oxidation temperatures to recover heat and to form a spent oil shale relatively free of carbon. Spend retorted oil shale which has been depleted in carbonaceous material is removed from the reactor and discarded. One well-known method of surface retorting is the Lurgi-Ruhrgas process.
In the Lurgi type retort, raw fresh shale is fed into a mixer wherein it is contacted with hot spent or partially spent shale. The combined oil shales are then fed into a zone for additional residence time. Shale oil which has been retorted from the oil shale is separated from the shale. The Lurgi process generally passes vapors from the screw mixer to product recovery, and solids from the screw mixer to a separation where additional hydrocarbon is recovered. The oil is recovered and the spent and partially spent shale is passed to a zone wherein carbon is burned off the shale. This can be done by introducing oxygen containing gas such as air or diluted oxygen, and sometimes additional fuel to the zone to combust the carbon. A preferred method is to pass the spent and partially spent shale, and air or air and fuel upwardly through a vertical elongated reactor such as a lift pipe. After oxidation, a portion of the spent shale is then removed from the flue gas from said zone, for example by electrostatic precipitators, and used for the manufacture of solid masses. Another portion of the spent shale is fed to the mixer to transfer heat to fresh oil shale. This process is more fully described in U.S. Pat. No. 3,655,518 which is incorporated by reference and made a part hereof.
During retorting, oil vapor leaves the solid mass as a saturated vapor (dew point) in both the screw mixer and surge hopper. If heat is lost, the higher boiling portion of the vapor can condense on spent shale, resulting in cracking and coking and lower liquid yield.
The mixture of solids from the screw mixer passing into the surge bin can cause countercurrent flow of spent solids and vapor, and lead to entrainment of heavy oil with the solids decreasing oil yield.
Positioning cyclone separators too far from the retorting zone, or in places where cyclone cooling occurs, can lead to oil condensation, and oil coking and cracking.
It is an object of this invention to provide an improved method and apparatus for the recovery of oil from oil shale, tar sands or oil containing diatomaceous earth.
It is an object of this invention to provide a hydrocarbon recovery process which minimizes heat loss and coking.
It is further an object of this invention to minimize oil condensation on solids and to maximize oil yield.